A waveform measurement and display apparatus, such as a transient recorder, waveform digitizer, or a digital storage oscilloscope, receives one or more analog electrical signals, converts such signals to digital form and stores them in waveform memory for subsequent retrieval and conversion back to analog form for display. Because the signals are digitized and stored, various processing and display modes may be implemented. For example, in a so-called pretrigger mode, signal segments which occur prior to a trigger event may be measured. Moreover, the stored waveforms may be processed by a computer to provide mathematical analysis thereof. For measuring graphic (or character) signals consisting of X (horizontal) and Y (vertical) coordinates, or for measuring timing components or phase relationships of two or more analog signals, an X-Y display may be provided.
In the case of a conventional waveform measurement apparatus which receives and digitizes two analog input signals and stores the digitized signals in two respective memory areas, the digital signals from the two memory areas are subsequently converted into analog output signals, and then applied respectively to the X-Y axes of a display device, such as a cathode-ray tube, to provide the X-Y display. However, it is often difficult to discern the time relationship between the two input signals from only the X-Y display. The conventional waveform measurement apparatus can display the two input signals simultaneously in a Y-T (wherein Y is amplitude and T is time) display mode so that the time relationship of the the two input signals may be analyzed. However, it is difficult to extrapolate a mental image of the X-Y display from the Y-T display of the two input signals. in addition, the conventional waveform measurement apparatus has the capability of expanding the Y-T display horizontally; that is, the time axis of the Y-T display can be expanded, but it is difficult to discern the time relationship between the expanded and unexpanded waveforms.